/Engine/Source/Editor/UnrealEd/Classes/Editor/EditorEngine.h
Returns the stored position at that index.
void GetWindowSizeAndPositionForInstanceIndex ( [ULevelEditorPlaySettings](API\Editor\UnrealEd\Settings\ULevelEditorPlaySettings) & InEditorPlaySettings, const int32 InInstanceIndex, const [FWorldContext](API\Runtime\Engine\Engine\FWorldContext) & InWorldContext, FIntPoint & OutSize, FIntPoint & OutPosition )